Condition monitoring, condition-based maintenance, and fault diagnosis of physical systems require a high probability of correct detection and isolation, a low false-alarm probability, and a timely decision on fault status. Fault diagnosis methods include model-free and model-based ones. Model-free based approaches include tools based on limit checking, visual analysis of data, plausibility analysis, Artificial Neural Network, and Fuzzy Logic.
A model-free approach may be capable of detecting a possible fault quickly, unraveling its root cause(s), and isolating it. Being free from the use of a model imparts an equally attractive freedom of the usual model-related difficulties such as identifying the required model, dealing with the presence of nonlinearities, and structural complexities.
However, these advantages are realized at a cost that could have various facets depending on the fault classification tool used. For neural networks, there is a lack of transparency, a need for a sufficient amount of training data covering most, if not all, operational scenarios, and a possibly lengthy training time. Fuzzy logic techniques, though less opaque than neural networks, suffer from the difficulty of deriving precise rules that distil an expert's knowledge of the application domain and which are necessary to drive the fuzzy inference engine. The model-based approach is based on the use of Kalman filtering, parity equation, system identification, and a diagnostic model.
A physical system is generally complex, nonlinear and the a priori information about the structure, based on the physical laws may not be available. For a large class of physical systems, a linearized model about some operating point may be employed, as it is mathematically tractable, and there are a wealth of readily available and powerful analysis and design tools. The linearized model, however, may not capture the behavior of the system over a wide range of operating regimes resulting from variations in the input and parameters of subsystems.
The foregoing “Background” description is for the purpose of generally presenting the context of the disclosure. Work of the inventor, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention. The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.